Organic Chemistry

332 CHAPTER 8 Reactions of Dienes • Ultraviolet and Visible Spectroscopy

c. d.

32. a. Give the products obtained from the reaction of 1 mole HBr with 1 mole 1,3,5-hexatriene.
    b. Which product(s) will predominate if the reaction is under kinetic control?
    c. Which product(s) will predominate if the reaction is under thermodynamic control?


33. 4-Methyl-3-penten-2-one has two absorption bands in its UV spectrum, one at 236 nm and one at 314 nm.
    a. Why are there two absorption bands?
    b. Which band shows the greater absorbance?


34. How could the following compounds be synthesized using a Diels–Alder reaction?

a. c.

b. d.

35. a. How could each of the following compounds be prepared from a hydrocarbon in a single step?
    
    
    1. 
       
       
       
       2. 
          
          
          
          3. 
             
          
          
          
          
       
       
       
       
    
    
    
    

b. What other organic compound would be obtained from each synthesis?

36. How would the following substituents affect the rate of a Diels–Alder reaction?
    a. an electron-donating substituent in the diene
    b. an electron-donating substituent in the dienophile
    c. an electron-withdrawing substituent in the diene


37. Give the major products obtained from the reaction of one equivalent of HCl with the following:
    a. 2,3-dimethyl-1,3-pentadiene
    b. 2,4-dimethyl-1,3-pentadiene
    For each reaction, indicate the kinetic and thermodynamic products.


38. Give the product or products that would be obtained from each of the following reactions:

a. b. CH CH 2 + CH 2 CH C CH 2 ∆

CH 3

CH CH 2 + CH 2 CH CH CH 2 ∆

HO CH 3

Br CH CH^3

3

OH

Br

O

O

CO 2 CH 3

O

O

CCH 3

4-methyl-3-penten-2-one

CH 3 CCH CCH 3

O CH 3

CH CH 2

+ HBr

CH 3

peroxide

CH CH 2

+ HBr

CH 3